The present invention relates to a filter carrier to be stacked for obtaining a filter tower, said filter carrier comprising a filter chamber defined by a bottom and a side wall for receiving a filter cake, a pressure-exerting plate which is formed on the bottom and which, when a plurality of filter carriers are superposed, engages at least partly into the filter chamber positioned thereunder for pressing the filter cake formed therein, at least one distributor element positioned below the pressure-exerting plate for distributing liquid to be filtered, and a seal for sealing between the pressure-exerting plate and the side wall of the filter carrier positioned thereunder.
Such a filter carrier is already known from PCT EP 92/01436, which originates from the same applicant. Filter carriers of this type are used for building a filter tower which may especially be used for sterile filtration in the beverage industry. When beer is being filtered, yeast cells and bacteria can be held back without preventing fine substances, which are responsible for the taste, from flowing therethrough.
The filter aid is supplied for precoating in a precoating station onto the filter carriers. The filter carriers are then superposed, thereby forming said filter tower.
The liquid to be filtered is then introduced laterally into the superposed filter chambers. To achieve a uniform distribution of the liquid to be filtered over the surface of the filter aid, a distributor element is arranged on the bottom of each filter carrier.
When the filter carriers are arranged one on top of the other, the bottom which is provided with a pressure-exerting plate and pertains to a filter carrier positioned thereabove engages in the manner of a pressure-exerting piece into the filter chamber of the filter carrier positioned thereunder and firmly presses the supplied filter aid. To prevent the filter aid and then the liquid to be filtered in the filtering process from escaping sideways, the pressure-exerting plate must be sealed relative to the inner wall of the filter chamber. To implement such a sealing, the known filter carriers are equipped--in the area of the side wall which defines the filter chamber--with annular grooves into which the O-ring seals are inserted. These O-ring seals seal the vertical walls of the pressure-exerting plate.
The distributor element which is held on the bottom side of the pressure-exerting plate is secured there with the aid of circumferentially arranged screws.
It is the object of the present invention to simplify such a construction and to increase wear resistance and functional reliability at the same time, with the high demands made on sterility being also met.
This object is attained in that the seal comprises both a sealing edge for sealing between the pressure-exerting plate and the side wall of the filter carrier positioned thereunder and a sealing collar for sealing and retaining the distribution element on the pressure-exerting plate.
This solution simplifies the construction on the whole because the seal performs three functions, namely sealing between the pressure-exerting plate and the side wall, holding the distributor element, and sealing the distributor element relative to the pressure-exerting plate. Since all of the three functions are fulfilled with the aid of a single component, i.e., a seal, the construction is simplified and the manufacturing costs are reduced to a considerable degree. Moreover, operative reliability is increased because the sealing collar also seals the distributor element.
The seal is lockingly held on the pressure-exerting plate in a very advantageous development of the invention. This arrangement of the seal is easy to implement. Moreover, fastening with screws is not necessary. This eliminates the possibility of the formation of deposits as are found in the prior art, with the deposits being very difficult to remove in the area of the screw connections and being undesired in view of the high demands made on sterility. The filter carriers and the filter towers of the abovementioned type have a circular shape as a rule. The seal is then formed as a surrounding sealing ring.
An impact-resistant and high-strength plastic material has been found to be especially suited as a material for the sealing ring. Such a plastic material is, e.g., the material that is commercially available under the name "Lauramid". This substance is a polyamide produced in a lactam casting process. Such a plastic material exhibits extraordinary dimensional stability and, in particular, a great notch impact strength and high creep resistance. As a result, the seal becomes resistant to wear, and the relatively rigid construction of the sealing edge has also the effect that, when the filter carriers are stacked one upon the another, the sealing edge performs a stripping action along the inner surface of the side wall in a reliable manner.
The sealing edge and the sealing collar are advantageously biased. This means that the arrangement of sealing collar and sealing edge in the installed state exerts a specific pressure on the inner surface of the side wall on the one hand and the distributor element on the other hand, which increases both the sealing action and the holding function.
A surrounding locking collar which snaps into a surrounding locking groove formed on the pressure-exerting plate is provided on the sealing ring for locking the sealing ring with the pressure-exerting plate. To mount the seal in an improved manner, the pressure-exerting plate passes from the mounting side to the locking groove into an inclined stop portion, so that when being arranged the seal is expanded in the area of the locking collar to the outside until the locking collar can snap into the locking groove inwardly.
The connection may be such that the sealing ring is captively held on the pressure-exerting plate and can only be removed by destruction. It would also be possible to make the sealing ring replaceable.
To achieve uniform inflow of the liquid to be filtered from the side, passage openings are circumferentially formed in the sealing ring for the liquid to be filtered. At a diameter of, e.g., 70 cm, it is sufficient to supply the liquid to be filtered with the aid of about 5 to 7 circumferentially distributed passage openings. This permits a uniform distribution above the filter chamber of the filter element postioned thereunder.
In another advantageous embodiment of the invention, a receiving groove for a surrounding outer seal is provided on the bottom opposite to the seal. The upper end of the side wall is thus received by two, approximately opposite sealing surfaces of the filter element positioned thereabove, and is reliably sealed against the exit of filter aid and/or liquid to be filtered.
In another embodiment of the invention, the upper edge of the side wall is formed with a beveled portion at least at the filter chamber side for centering the sealing ring. This permits an automatic centering operation during stacking after an initial coarse alignment of sealing rings relative to the filter chamber positioned thereunder whenever an upper filter carrier is inserted with the pressure-exerting plate into the upper portion of the filter chamber of the filter carrier positioned thereunder.
In another advantageous embodiment of the invention, the sealing edge is arranged on the seal opposite to the sealing collar. The forces applied to the sealing collar and the sealing edge thereby compensate each other in part at the point of impact between sealing edge and sealing collar, which further increases the stiffness and thus the reliability of the seal.